As some experience shows  , accident happens when people are authorized to push the code themselves (after diff review or not ...).
It may be times to discuss some contribution policy adaptations.
Discussion happened on irc some time ago between @zack, @nahimilega and me. Possible policies so far:
- (current) contributor can push once the diff is reviewed and accepted.
- contributor never pushes. Staff member pushes once the diff is reviewed 
Please feel free to amend the description ;)
 We'll then have to discuss the git adaptations needed (git commit message format, merge policy, etc...).